1. Field of the Invention
The present invention relates generally to a Bluetooth system, and in particular, to a method for setting up a communication link between Bluetooth devices in a Bluetooth system.
2. Description of the Related Art
The Bluetooth standard has been introduced to provide low-cost, short-range wireless communication between mobile devices such as a portable PC (Personal Computer) and a mobile phone. The Bluetooth standard enables wireless voice/data communication between various digital devices, using a radio frequency. For example, a mobile phone and a notebook computer (a portable PC), when employing the Bluetooth technology, can be wirelessly connected to each other without using a cable. The Bluetooth technology is applicable to all kinds of digital devices, including a PDA (Personal Digital Assistant), a desktop computer, a FAX (facsimile), a keyboard and a joystick.
FIG. 1 illustrates a network structure of a conventional Bluetooth system. As illustrated in FIG. 1, the Bluetooth system supports point-to-point and point-to-multipoint connections. Devices sharing one channel should also share a channel capacity, and a set of these devices is called a “piconet”. That is, the piconet is defined as a set of devices connected to one another through a Bluetooth ad-hoc network. In general, one piconet includes 7 devices: one of the 7 devices serves as a master for performing piconet management operations such as the generation of a frequency hopping pattern, while the remaining devices serve as slaves.
Hereinafter, reference will be made to a piconet forming process. In a standby state where devices are disconnected from one another, each device receives a new message every 1.28 second. When a device receives a connection request message from other devices, the device serves as a master and starts to identify other devices by exchanging Inquiry and Page messages. At this point, the devices assigned an 8-bit park address enter into a park state. The devices in communication with the master are then assigned a 3-bit active address to get into an active state, which results in the formation of a piconet. Since one of 8 (=23) addresses is used as a broadcasting address, 7 devices assigned the remaining 7 addresses constitute one piconet.
The active state is subdivided into three modes: an active mode, a hold mode and a sniff mode. In the active mode, the devices actually communicate with one another. In the hold and sniff modes, the devices participate in a piconet but do not influence the whole traffic of the piconet. The master transmits an Inquiry message including an access key at 625 μs intervals, and is synchronized with a slave within 2 seconds.
Upon receiving a Page message from the master after being assigned a 3-bit active address, the slave is synchronized with the master through a hopping pattern determined by the master. The master and the slave then perform an authentication process on each other. A password key used for the authentication is obtained by XOR-gating a random number generated by the master and an MAC (Medium Access Control) address of the slave. When the authentication process is completed, data can be communicated between the master and the slave. The master controls all of the traffic on a channel.
A scatternet is comprised of a plurality of independent, non-synchronized piconets. Users of each piconet have a unique 1 MHz hop channel in the scatternet. Since the users of the piconet do not share their unique 1 MHz channels with the users of other piconets, the total throughput increases with the number of the piconets. In addition, while a device serves as a slave in one piconet of the scatternet, the device can also serve as a master in another piconet.
However, referring to FIG. 1, the conventional Bluetooth system does not provide a function for linking a master 1 in a piconet A to a Bluetooth device in a piconet C. As a result, the master 1 cannot communicate with the devices in piconet C. Therefore, the conventional Bluetooth system has a flaw in that a Bluetooth device can only communicate with other Bluetooth devices in its piconet area, and cannot communicate with the Bluetooth devices in another piconet area.